The present invention relates to a plasma etching apparatus and etching method and, more particularly, to a plasma etching apparatus and etching method suitable for forming a fine pattern in the semiconductor manufacture process.
In the semiconductor manufacture process, the plasma etching apparatus is widely used in the fine processing processes, for example, such as film deposition, etching, and ashing. The process by plasma etching performs the predetermined process by making processing gas introduced into the vacuum chamber (reactor) plasmatic by the plasma generation means, performing the fine processing by making it react on the surface of a semiconductor wafer, and discharging volatile reaction products.
In this plasma etching process, the temperatures of the inner wall of the reactor and wafer and the deposition status of reaction products on the inner wall greatly affect the process. If reaction products deposited inside the reactor are peeled off, dust may be caused, resulting in deterioration of the element characteristics and reduction of the yield.
Therefore, in the plasma etching apparatus, to keep the process stable and control generation of foreign substances, it is important to control the temperature in the reactor and deposition of reaction products on the surface.
For example, in Japanese Patent Application Laid-Open 8-144072, for the purpose of improving the selection ratio in the dry etching process of a silicon oxide film, a dry etching apparatus for controlling and holding the temperature of each unit inside the reactor at a high temperature within a range of 150.degree. C. to 300.degree. C. (desirably from 200.degree. C. to 250.degree. C.) which is higher than the temperature at the etching stage of 150.degree. C. or more with the accuracy of less than .+-.5.degree. C. is described. When the temperature of each unit of the inner surface of the reactor is increased and controlled at a high value by heating like this, the deposited amount of plasma polymeric products on the inner surface of the reactor reduces, and the deposited amount of plasma polymeric products on a semiconductor wafer increases, and the selection improves.
In Japanese Patent Application Laid-Open 5-275385, a parallel plate type plasma etching apparatus in which a heating means for increasing and keeping the temperature so that reaction products generated by the plasma etching will not be deposited is installed on at least one of the clamp ring (workpiece holding means) and focus ring (plasma centralization means) is described. As a heating means, a resistance heating element is used. Deposition of reaction products can be prevented by heating, so that peeling of reaction products and deposition of particles on the surface of a workpiece can be reduced.
As mentioned above, in the plasma etching apparatus, it is important to control the temperature of the surface of the inner wall of the chamber and deposition of reaction products on the surface of the inner wall.
However, when the temperature of the inner wall surface of the chamber, particularly the temperature of the side wall surface having a wide area is set to a high value between 200.degree. C. and 250.degree. C. or more, the etching characteristic becomes very sensitive to the temperature of the inner wall surface and a problem arises that the reproducibility and reliability of the process are apt to reduce.
For example, in S. C. McNevin, et al., J. vac. Sci.
Technol. B 15(2) March/April 1997, p. 21, Chemical challenge of submicron oxide etching, it is indicated that when the side wall temperature changes from 200.degree. C. to 170.degree. C. in inductive coupling plasma, the oxide film etching rate increases more than 5%. As a reason, it is inferred that since the side wall temperature lowers, much more carbon is adsorbed into the wall, and deposition of carbon on a wafer reduces, and the oxide film etching rate increases. As mentioned above, since high density plasma, particularly, performs a strong interaction with the inner wall of the reactor in the high temperature zone, deposition of reaction products on the inner wall surface and composition change of the surface proceed rapidly due to a change in the temperature balance inside the reactor and appear as a change in the etching characteristic.
Furthermore, in the high temperature zone, the aforementioned interaction between the plasma and the inner wall becomes very sensitive to a change in temperature. For example, when SiO2 is used as a material of the inner wall surface, a thermodynamic relationship between the etching rate by F atoms of SiO2 and the wall temperature is reported (D. L. Flamm, et al., J. Appl. Phys., 50, p. 6211 (1979)), and when this relationship is applied to a temperature zone of more than 150.degree. C., the etching rate rapidly increases exponentially when the wall temperature is between 200.degree. C. and 250.degree. C. or more.
Therefore, in such a high temperature zone, the temperature control requires high accuracy such as .+-.5.degree. C. max. However, the inner wall surface is exposed to high density plasma, so that it is not easy to control the wall surface temperature with high accuracy in such a high temperature zone. To realize it, a temperature detection means and a heating means such as a heater and lamp are used for temperature control, though the temperature control mechanism and means are largely scaled. Furthermore, in such a high temperature zone, reaction products are not deposited on the inner wall surface, so that the wall surface is etched and consumed by plasma. Therefore, it is necessary to periodically exchange the parts of the inner wall surface and an increase in the cost of expendable supplies results. Heating requires large energy, thus the high temperature zone is not desirable also from a viewpoint of energy consumption.
The same problem is imposed also by heating the ring around a wafer and the electrode. When the ring is heated to increase the temperature thereof, deposition of reaction products can be prevented, though the heating mechanism such as the resistance heating element makes the equipment constitution complex. When the ring and inner wall surface are etched and consumed by plasma even if deposition of reaction products can be prevented, there is the possibility that the constitution material itself will become a new dust source. Furthermore, when the parts of the ring and inner wall surface are consumed, it is necessary to periodically exchange them and the running cost of the equipment increases.
One method for solving such a problem is to protect the inner wall surface of the chamber by a surface coating layer of a polymer. For example, in Japanese Patent Application Laid-Open 7-312363, a plasma etching apparatus for keeping the temperature of the workpiece (article to be processed) holder higher than that of the wall surface of the chamber and forming a surface coating layer on the inner wall surface of the chamber is described. By catching and storing contaminant particles in a polymer film, remaining and storing of contaminants in the chamber due to reaction products can be reduced.
However, the purpose in this case is not to protect the wall surface but to catch contaminant particles. It is just described that the temperature for forming a surface coating layer on the inner wall surface of the chamber is lower than that of a workpiece (article to be processed) by more than 5.degree. C. and the temperature range and control accuracy are not taken into account. The pressure range is a high pressure range such as several hundreds mtorr (several tens Pa). However, it is inferred that the deposition temperature of a film changes the composition and quality of the film and affects the film peeling strength and occurrence of foreign substances. It is expected that changing of the deposited film temperature results in occurrence of cracking and peeling due to repetition of thermal expansion and shrink and causes foreign substances and the temperature control accuracy is an important factor. Within a pressure range of several tens mtorr max. (several Pa max.), it is considered that the film deposition condition varies due to high ion energy and a longer mean free distance of molecules, Furthermore, in the aforementioned prior art, it is necessary to remove the coating layer catching contaminants from the wall surface of the plasma etching chamber and it directly affects the throughput of the equipment and the cost of expendable supplies. However, this respect is not taken into account.